Silicon-containing films are used for a wide variety of applications in the semiconductor industry. Silicon-containing films include silicon films such as polycrystalline silicon (poly-Si) and epitaxial silicon, silicon germanium (SiGe), silicon germanium carbide (SiGeC), silicon carbide (SiC), silicon nitride (SiN), silicon carbonitride (SiCN), and silicon carboxide (SiCO). Various physical and/or chemical deposition techniques are routinely employed for silicon-containing film deposition, and often more than one technique may be used to deposit a particular film. The preferred deposition method is determined by considering the desired film properties, physical and/or chemical constraints imposed by the device being fabricated, and economic factors associated with the manufacturing process. The selected process is often the one that provides an acceptable trade-off to address the pertinent technical and economic concerns.
Thermally excited chemical vapor deposition (CVD) is a common technique used to deposit materials for integrated circuit fabrication. In a typical embodiment, a substrate (wafer) is placed in a low-pressure process chamber and maintained at a controlled temperature. The substrate is exposed to gaseous ambient of one or more precursors that contain the chemical elements to be incorporated in the film. The gaseous precursors are transported to the substrate surface and combine via one or more chemical reactions to form a solid film. The conditions of the reactor chamber, substrate, and precursor are typically chosen to favor chemical reactions that produce films with the desired physical, chemical, and electrical properties.
A plasma can be employed to alter or enhance the film deposition mechanism. A deposition process that employs a plasma is generally referred to as a plasma-enhanced chemical vapor deposition (PECVD). In general, a plasma is formed in a vacuum reactor by exposing a gas mixture to a RF signal and exciting electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the excited electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber.
Plasma excitation generally allows film-forming reactions to proceed at temperatures that are significantly lower than those typically required to produce a similar film by thermally excited CVD. In addition, plasma excitation may activate film-forming chemical reactions that are not energetically or kinetically favored in thermal CVD. The chemical and physical properties of PECVD films may thus be varied over a relatively wide range by adjusting process parameters.
SiN has been widely used in semiconductor devices as a passivation film, a diffusion barrier, and an etch-stop film. Device quality SiN films have been deposited by PECVD using silane (SiH4) and ammonia (NH3) or thermal CVD using dichlorosilane (SiH2Cl2) and NH3. However, the explosive behavior of SiH4 and corrosive behavior of SiH2Cl2 requires strict control over processing conditions and careful handling of the process effluent. Furthermore, deposition of SiN films from SiH2Cl2 require high deposition temperatures that are incompatible with advanced device processing requiring a low thermal budget. New low-thermal CVD processes have been developed for depositing SiN films using bis-(tert-butylamino)silane (BTBAS) and hexachlorodisilane (HCD) but alternative deposition methods are required that can provide improved device performance, lower thermal budget, and reduced maintenance of the processing system.